Cornelis Gijsbert Gerrit Jan van Steenis (31 October 1901 – 14 May 1986) was a Dutch botanist.
Van Steenis wrote many publications on the flora of the Maritime Southeast Asia region, among others about taxonomy and plant geography.
From 1935 to 1942, he was co-editor of De Tropische Natuur, the magazine of the Dutch East Indian Natural History Society.
In 1948 and 1950, he took up Heinrich Zollinger's 1857 recognition of Malesia as a floristic region in the Paleotropical kingdom, and expanded it.
On 5 June 1950 he was elected a corresponding member of the Royal Netherlands Academy of Arts and Sciences, but cancelled his membership on 1 December of that year.